While basal pterosaurs had lots of teeth, and certain derived pterosaurs, like SoS 2179 and Pterodaustrohad dozens to hundreds of teeth, certain pteroaurs appear to have been toothless – or so they say…

I’ll just cut to the chase.
Apparently “toothless” pterosaurs, like Pteranodon, Nyctosaurus and Tapejara actually had one tooth at the tip of the premaxilla and one tooth at the tip of the dentary. That’s how the tips were able to become and remain so sharp. Like the wing ungual and manual digit V, these single teeth have been overlooked by all prior pterosaur workers. The evolution of these single anteriorly-directed teetth can be documented in predecessor taxa among the germanodactylids, but it is still not clear whether one tooth became smaller or the two anterior teeth fused to become one. It seems reasonable that these teeth would be replaced with new teeth at the root, but this has not yet been documented. In the images below, if there was a “next” tooth, it is not apparent.

Figure 1. Click to enlarge. The tooth at the tip the mandible of KUVP 66130, a nyctosaurid.

Figure 2. Click to enlarge. The tooth at the tip of the rostrum of KUVP 66130, a nyctosaurid.

In the nyctosaurids above the dentary and premaxillary tooth tips are shown.

Figure 3. Click to enlarge. The tooth at the tip of the rostrum of Tapejara.

The Evolution of “Toothless” Pterosaurs
In several pterosaurs the medial or first premaxillary tooth was procumbent. It angled forward as well as downward. In B St 1967 I 276 (No. 6 of Wellnhofer 1970), the tiniest pterosaur, the anterior premaxillary tooth was procumbent.

Figure 4. The rostrum of No. 6 in which the teeth at the tip were procumbent, but not anteriorly oriented.

In the specimen from the Senckenberg-Museum Frankfurt a. M. No. 4072, (No. 12 of Wellnhofer 1970) the anterior tooth was oriented further anteriorly and may have been a single tooth.

Figure 5. The jaw tips of No. 12

In Germanodactylus the SMNK-PAL 6592 specimen, the anterior premaxillary and dentary teeth were fully anterior in orientation.

Prequel: Longisquama Gets No Respect
(or the Lengths Scientists Will Go to Protect Pet Theories)
In their two-part paper on pterosaur origins Hone and Benton (2007, 2008) announced they would test whether pterosaurs nested more parsimoniously within the Archosauria (Bennett 1996) or the Prolacertiformes (Peters 2000). They used the technique of the supertree, gathering several trees together to come up with a larger, ostensibly more complete, tree. That permitted them to use the data of others without having to visit fossils. We’ll get back to their results (below), but first a short background study.

Peters (2000) tested the matrices of Bennett (1996) and two others (Jalil 1991 and Evans 1986) simply by adding Langobardisaurus and the fenestrasaurs, including Cosesaurus, Sharovipteryx and Longisquama. Pterosaurs nested with these taxa, rather than any archosaur or archosauromorph, when given the opportunity. Peters (2000) erected the clade, the Fenestrasauria, because they shared the trait of an antorbital fenestra without a fossa, convergent with that of archosaurs.

Getting Back to Where We BeganHone and Benton (2007) discredited the data of Peters (2000) and elected not to include any of it in their supertree. That left only one study that included pterosaurs, Bennett (1996), in their supertree analysis. Having eliminated the opposing candidate data and the opposing candidate taxa, the results were predetermined. The results of Hone and Benton (2008) reflected the results of Bennett (1996). Sadly, the results also nested members of the Choristodera far from the Choristodera and members of the Lepidosauromorpha far from the Lepidosauromorpha, so the study had its problems. Moreover, Hone and Benton (2008) falsely gave credit for the prolacertiform hypothesis to Bennett (1996), after properly giving it to Peters (2000) in their earlier (2007) paper. And now you know the lengths scientists will go to protect their pet theories.

The Back Half of Longisquama
Ever since Sharov (1971) reported that only the front half of Longisquama was visible, scientists stopped looking for it. Ironically, one of the plumes illustrated by Sharov(1971), the one not radiating like the others, was a tibia and femur. The subdivided “feather shafts” reported by Jones et al. (2000) were actually displaced toes subdivided by phalanges. Here, using the technique of DGS (digital graphic segregation) the back half of Longisquama is, at last, revealed.

Figure 2. Click to enlarge. The complete fossil of Longisquama.

The back half of Longisquama was overlooked for so long because the elements lined up with and were camouflaged by the plumes. Apparently Longisquama’s stomach exploded, or was torn up. The front third of Longisquama is undisturbed, the tail is undisturbed, but the hips are turned backwards and the legs and feet are rotated up to the dorsal vertebrae.

Figure 3. Longisquama in lateral view, dorsal view and closeup of the skull. Like Microraptor, Longisquama glided/flew with similarly-sized wings both fore and aft.

Distinct from CosesaurusThe skull of Longsiquama had a more constricted snout, which enhanced binocular vision. The orbits were larger. The teeth had larger cusps. The naris was probably larger. With increased bipedalism and active flapping, Longiquama probably experimented with aerobic metabolism. The cervicals were shorter and the dorsal series was longer, especially so near the hips and between the ilia. The sacrum curved dorsally 90 degrees, which elevated the attenuated tail. These vertebral modifications made Longsiquama similar to a lemur, which also leaps from tree to tree. Such a long torso provided more room for plumes, gave the back great flexibility, and provided more room for egg production. The pectoral girdle was little changed from Cosesaurus. The clavicles curved around the sternal complex and the sternal keel was deeper. Fused together the interclavicle, clavicles and sternum form a sternal complex, as in pterosaurs. During taphonomy the sternal complex ofLongisquama drifted to beneath the cervicals, exactly where the clavicles are found in non-fenestrasaur tetrapods, including birds. This has led to confusion because the clavicles overlapped giving the appearance of a bird-like furcula. As in Cosesaurus, the pterosaur-like pectoral girdle and socketed coracoids enabled Longisquama to flap and generate thrust during leaps. The pelvis was greatly elongated anteriorly and posteriorly with a posterior ilium rising along with the dorsally curved sacrum of seven vertebrae. The pubis and ischium were much deeper, which provided a much larger pelvic aperture to pass a much larger egg. The distal femur was concave and the proximal tibia convex, as in Sharovipteryx. Both the femur and tibia/fibula were more robust. The foot was relatively large with digits of increasing length laterally. Pedal digit V had a curved proximal phalanx.

Longisquama is famous for, and was named for, its dorsal plumes. Another set of plumes arose from its skull and neck. Former caudal hairs (in Cosesaurus) formed a tail vane in Longisquama. As in Sharovipteryx and pterosaurs, Longsiquama had a uropatagium trailing each of its hind limbs. Like Cosesaurus, Sharovipteryx and pterosaurs membranes trailed the forelimbs, too. This documents the origin of the pterosaur wing and proves that it developed distally on a flapping wing (Peters 2002) rather than proximally as a gliding membrane (contra Elgin, Hone and Frey in press) and certainly without wing pronation, loss of digit V, loss of ungual 4 and migration of metacarpals I-III to the anterior face of metacarpal IV (contra Bennett 2008).

Longisquama was overloaded with secondary sexual characteristics. From plumes to flapping arms, Longisquama was all about creating an exciting presentation unrivaled until the present-day bird-of-paradise. Longisquama had everything Cosesaurus had, only wildly exaggerated. With increased bipedalism and active flapping, Longiquama probably experienced the genesis of aerobic metabolism.

The Origin of the Pterosaur Wing
The elongated and robust finger four of Longisquama was also overlooked by all prior workers. Reconstructed here the hand of Longsiquama remains the best transitional example between Cosesaurus and pterosaurs. It is likely that digit 4 did not flex with the other three fingers in Longisquama because the PILs (parallel interphalangeal lines) were not continuous through digit 4, which also supported a pterosaur-like wing membrane, preserved along with the other soft tissue, the plumes.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

Wikipedia reports:“Ichthyosaurs thrived during much of the Mesozoic era; based on fossil evidence, they first appeared approximately 245 million years ago (mya) and disappeared about 90 million years ago, about 25 million years before the dinosaurs became extinct. During the middle Triassic Period, ichthyosaurs evolved from as-yet unidentified land reptiles that moved back into the water, in a development parallel to that of the ancestors of modern-day dolphins and whales.”

Well, here we’re going to identify those “unidentified” land animals as the ancestors of ichthyosaurs: They’re mesosaurs.

It’s not difficult to figure out which reptiles were the closest to ichthyosaurs. All you have to do is include representatives from all the major groups and run their characters through phylogenetic analysis. The ones most like ichthyosaurs will nest on a tree closest to ichthyosaurs. Such a study has never been undertaken before. Typically a few suprageneric (above the level of genus) taxa are chosen. This gives no opportunity for individual genera within a larger clade to step up to the plate and nest as sister taxa. This also allows cheating, the ability to cherry pick traits from several taxa within a clade to create a chimaera taxon.

Here’s the tree I used (and it keeps growing and growing):

Figure 2. The Reptile Family Tree and the Evolution of Ichthyosaurs. Here you can trace the evolution of ichthyosaurs (represented by Utatsusaurus) all the way back to Ichthyostega.

Past Mistakes Based on Using Suprageneric Taxa
Motani (1998) linked ichthyosaurs to Younginiforms or to Coelurosauravus (a gliding reptile) through Saurosternon. Unfortunately, Motani used suprageneric taxa and did not include mesosaurs.

Maisch (2010) nested ichthyosaurs either with mesosaurs within the diapsida (which is generally correct) or with Procolophon, an anapsid turtle sister. The connection was never spelled out, perhaps because of his use of suprageneric taxa. In fact, Maisch threw up his hands when he reported, “In the case of the ichthyosaurs we know that they are amniotes, and that they are not synapsids… Whether ichthyosaurs are diapsids, and if so, where exactly they have to be placed within the Diapsida, or whether they are parareptiles, and if so, whether they are related to mesosaurs or not, these are questions that remain as unresolved as one hundred years ago.”

Figure 2. Click to enlarge. The origin of ichthyosaurs and thalattosaurs from basal diapsids and basal mesosaurs. Relationships are rather apparent when seen in this context.

Here is the Ancestral Lineage of IchthyosaursStarting with the basal diapsid,Petrolacosaurusand moving toward the basal enaliosaur, Claudiosaurus, the skull size was reduced (but probably not to the extents seen in Claudiosaurus) and the limbs become smaller and probably webbed. Hovasaurus was a sister to Claudiosaurus. Small-skulled Pachypleurosaurus was another sister to Claudiosaurus that nested at the base of the Sauropterygia.

Stereosternum is a somewhat forgotten taxon, but it represents a basal mesosaur, before all the temporal fenestra were closed off. The skull was not so small, the rostrum was elongated and the ribs became thicker. Mesosaurus was a derived sister, but too specialized in a different direction.

Wumengosaurus was considered an odd pachypleurosaur (Wu et al. 2011), but Wumengosaurus nests closer to the base of the ichthyosauria including Hupehsuchus. The quadratojugal was greatly reduced, eliminating the lower temporal bar, as in sauropterygians and ichthyosaurs.

Askeptosaurus was a thalattosaur, a sister taxa to the ichthyosaurs. Overall it retained the shape of a mesosaur, but the skull openings were reduced on top and expanded to the sides.

Hupehsuchus is a basal ichthyosauriform specialized without teeth. Even so it is the closest sister taxon known to basal ichthyosaurs represented by Utatsusaurus, a basal ichthyosaur.

In Summary
The long term trend in the evolution of ichthyosaurs was to enlarge the body overall, elongate the rostrum, shorten the neck, deepen the torso, reduce the thickness of the ribs, shorten the tail and give it a dorsal kink, reduce the limbs and turn them into paddles.

There is no more parsimonious solution among the tested reptiles. And the resemblances between each sister taxon are in line with the small steps that evolution takes. You can read more details starting here.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

Figure 1. Mesosaurus up to 1 meter in length, was long considered an anapsid, but the temporal fenestrae were secondarily infilled from a basal diapsid configuration, as in Claudiosaurus.

Mesosaurus is a Problem for Paleontologists
Here’s the paradigm: Despite its many derived traits, Mesosaurushas long been nested with various other basal reptiles. This long-snouted, needle-toothed, aquatic Permian reptile apparently had no temporal fenestrae, according to Modesto (2006, 2010) and others. Therefore Gauthier (1988) and Modesto (1999) nested Mesosauridae with other such taxa, members of the Captorhinidae and Millerttidae, two basal herbivores without an aquatic niche. Laurin and Reisz (1995) nested Mesosauridae between synapsids and turtles. Laurin and Reisz (2004) nested Mesosaurus with Acleistorhinus (Figure 2), another herbivore sister to Milleretta. None of these proposed taxa even vaguely resemble mesosaurs. None of these studies included Claudiosaurus, ichthyosaurs and thalattosaurs.

Figure 2. Mesosaurus (left) and Acleistorhinus (right) were nested as sister taxa by Laurin and Reisz (2004) despite their many differences. Claudiosaurus and other enaliosaurs were not included in that study.

Not an Anapsid, but a Diapsid
A reconstruction of Mesosaurus (Figure 1) appears to retain at least a sliver of a lateral temporal fenestra. A reconstruction of the more primitive and typically ignored Stereosternum, another mesosaur, appears to retain a complete diapsid configuration. A reconstruction of yet another mesosaur, Wumengosaurus, retains a diapsid configuration, but with the loss of the lower temporal bar by reduction of the quadratojugal.

The CleithrumMesosaurus had a tiny cleithrum, a sliver of bone dorsal to the clavicle on the leading edge of the scapula. It shares this trait with Petrolacosaurus and Claudiosaurus.

The Limbs
The structure of the ankles made walking on land impossible, thus relatives should be looked for among aquatic taxa, not terrestrial herbivores, like Acleistorhinus

It Takes a Larger Study
A larger study of reptiles, and the largest one so far, nests Stereosternum within the basal aquatic diapsids, between Claudiosaurus, and Wumengosaurus, which was basal to ichthyosaurs and thalattosaurs. Other studies did not offer mesosaurs the opportunity to nest elsewhere. When you expand the inclusion list, as was done here, the opportunity for a correct nesting increases.

Figure 2. The nesting of the mesosaur, Stereosternum, in the Reptile Family tree at the base of the aquatic clade, the Enaliosauria.

Below are skeletal images of the sisters of Mesosaurus in phylogenetic order. The similarities are obvious and follow a gradual evolutionary sequence. The reduction and closure of the temporal fenestrae are also found in sister taxa including Araeoscelis and Pachypleurosaurus(not shown here).

Figure 3. The sisters of Mesosaurus from the basal diapsid, Petrolacosaurus to the basal ichthyosaur, Utatsusaurus.

Check out the various taxon names in www.reptileevolution.com for more details. As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

We’ll Continue with BrasileodactylusBrasileodactylus araripensisAMNH 24444 (Kellner, 1984; Veldmeijer 2003b) was originally described from just the anterior jaws and later a complete skull and other elements were found. It was derived from a sister to Coloborhynchus and Haopterus(see part 1), skipping the istiodactylid clade (part 2). Distinct from Coloborhynchus, the skull of Brasileodactylus had no crest. The posterior premaxillary teeth were quite long. So were the matching dentary teeth. The squamosal had a dorsal process that gave the lateral temporal fenestra the appearance of a human ear. The lacrimal protruded into the orbit. The jugal was expanded anteriorly into the antorbital fenestra. The antorbital fenestra was shorter.

Barbosania Barbosania gracilirostris (Elgin and Frey 2011) was considered close to Brasileodactylus and was similar in size. The original report stated, “While elements of the cranium appear to suture very early in ontogeny (Kellner and Tomida 2000) all ornithocheiroids recovered from the Romualdo Member of the Santana Formation are considered to be ontogenetically immature based on the lack of fusion in the postcranial skeleton.” Actually this is a phylogenetic signal. As derived lizards, pterosaurs did not follow archosaur fusion patterns.

Figure 2. Click to enlarge. Ludodactylus.

LudodactylusLudodactylus sibbicki SMNK PAL 3828 (Frey, Martill and Buchy 2003) is known from a skull with the unusual combination of a cranial crest and teeth. Distinct from Brasileodactylus, the skull of Ludodactylus was shorter overall with a parietal (cranial) crest with a frontal leading edge. The jugal was not expanded into the antorbital fenestra. The orbit was narrower. The postorbital was more robust. The mandible was more robust and was upturned anteriorly with smaller teeth posteriorly.

CearadactylusCearadactylus atroxformerly: SMNK PAL 3828 and CB-PV-F-O93, now: UFRJ MN 7019-V (Leonardi and Borgomanero 1985) Cenomanian, Early Cretaceous, ~90 mya, ~57 cm skull length is known from a skull with an unusual history. Originally it was put together with the premaxilla and anterior dentary switched. Distinct from Brasileodactylus, the skull of Cearadactylus had a wide spoonbill or rosette tip from which erupted giant teeth. The maxillary teeth were tiny. The mandible was deeper, but flatter anteriorly.

Cearadactylus ligabuei CCSRL 12692/12713 (Dalla Vecchia 1993) was similar but had a distinctly shorter rostrum and smaller teeth with an upturned premaxilla. The tip was not a spoonbill, but the middle of the rostrum was narrowed or pinched in dorsal view. The jugal was more gracile.

Figure 3. Click to enlarge. Liaoningopterus

LiaoningopterusLiaoningopterus guiIVPP V 13291 (Wang and Zhou 2003) Cenomanian, Early Cretaceous, ~90 mya, ~61 cm skull length. Distinct from Cearadactylus, the skull of Liaoningopterus was low anteriorly and very tall posteriorly. A very low crest surmounted the snout tip. Only one premaxillary tooth was enlarged to fang status. It is the largest tooth known for any pterosaur. The anterior dentary was expanded.

Figure 4. Click to enlarge. Anhanguera.

AnhangueraAnhanguera piscatorIVPP V 13291 (A. bittersdorffi No. 40 Pz-DBAV-UERJ Campos & Kellner, 1985; A. santanae AMNH 22555 Wellnhofer 1985; A. piscator, Kellner and Tomida 2000) Aptian, Early Cretaceous ~110 mya, ~60 cm skull length. Distinct from Liaoningopterus, the skull of Anhaguera had a longer premaxillary crest and smaller teeth. The anterior dentary formed a keel. The squamosal did not rise to form an “ear” shape of the lateral temporal fenestra. The tail was robust and had elongated vertebrae distally. Distinct from Brasileodactylus, manual 4.1 extended to the elbow when folded. Postcranially Anhanguera was most similar to SMNS PAL 1136, but without such a deep sternal complex keel and deep torso. The foot had very short metatarsals and elongated phalanges.

In Summary
The Ornithocheiridae is one of the few pterosaur clades without tiny members. Then again, from Yixianopterus at the base to Anhanguera as the most derived taxon, the morphology of this clade did not go through major changes. Trends toward the development and loss of a snout tip crest, more robust forelimbs and more gracile hindlimbs, an increase in the size of the antorbital fenestra in istiodactylids are all apparent. From the wing/leg ratios it seems apparent that this clade spent more time on the wing and less on the ground. Take-off was likely into the wind with a minimum take-off run from locations near steady and constant ocean breezes. A lack of skeletal fusion (sacrals, scapula/coracoid) permeates this clade, with some of the largest specimens lacking fusion. Fusion did affect some members, but the pattern was phylogenetic, not ontogenetic. The warped deltopectoral crest exhibited by some ornithocheirids has linked them to Pteranodon, but the morphology is distinct and the development was by convergence.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

In part 1 of the Ornithocheiridae we looked at the base of this large clade of long-winged soaring pterosaurs. Here in part 2 we’ll look at Coloborhynchus, Istiodactylusand their kin. These taxa form a clade of their own, a little off to the side. In part 3 we will start again where we ended in part 1 and examine more derived taxa such as Anhanguera and Liaoningopterus.

Figure 1. The Ornithocheiridae. Click to enlarge and expand.

We’ll Continue with ColoborhynchusColoborhynchus spielbergi(Owen 1874, = Ornithocheirus clavirostris; C. spielbergi Veldmeijer 2003) RGM 401 880, Early Cretaceous was originally lumped with Ornithocheirus and much later was considered congeneric with Anhanguera by several workers (Kellner 2006). Distinct from Haopterus, the skull of Coloborhynchus had an anterior crest both above the snout and below the chin. The pre-antorbital fenestra region was longer. The orbit was narrower and raised higher over the antorbital fenestra. The neural spines were taller. A notarium was formed by several fused dorsals into which the scapula was articulated. The sacrals were interlocked if not fused. The sternal complex was rather deep. The scapulocoracoid was fused. The humerus was much more gracile. The ulna and radius were also thinner, but the distal ends were expanded. The pelvis was more robust with a more ossified ischium and a raised posterior ilium.

Criorhynchus Criorhynchus mesembrinus(Owen 1874, = Ornithocheirus clavirostris; = Tropeognathus mesembrinus, Fastnacht 2001)BSp 1987 I 46 from the Early Cretaceous was a sister to Coloborhynchus and may be congeneric with it. Distinct from Coloborhynchus, the skull of Criorhynchus was longer, lower and wider. The palatal elements were more robust. The ischium was narrower.

Nurhachius, a Basal IstiodactylidNurhachius ignaciobritoi(Wang, Kellner, Zhou & Campos 2005)IVPP V-13288, Early Cretaceous, skull length ~30 cm, ~2.5 m wingspan. Distinct from Criorhynchus the skull of Nurhachius further extended the rostrum and increased the size of the antorbital fenestra. If predecessors had a crest, it was greatly reduced or underdeveloped in Nurhachius. The orbit was very narrow and posteriorly slanted with a tiny sclerotic ring at the top. The upper temporal fenestra was completely above the orbit. Distinct from Coloborhynchus, the sternal keel was very deep (if that is the keel). The humerus was shorter. Fingers 1-3 were smaller. The femur was shorter. The metatarsals were robust and the pedal digits were slender, as in Zhenyuanopterus.

One of the Biggest Ornithocheirids Still Has No NameSMNK PAL 1136 (not yet described, figured by Frey and Marill 1994) ~80 cm skull length, Aptian, Early Cretaceous ~130 mya, was originally considered an Anhanguera sp. Larger and distinct from Istiodactylus, the skull of SMNK PAL 1136 had the antorbital fenestra extend into the anterior rostrum just posterior to the premaxillary crest. The orbit was high and small. It was located just aft of the mandibular articulation. The jugal + lacrimal were reduced to slender rods oriented dorsoposteriorly. The sternal complex had a large keel and a reduced sternal plate. The scapulocoracoid was gracile. The gracile humerus expanded distally. Manual 4.1 extended to the elbow when folded. The pelvis was relatively smaller than in Coloborhynchus and the prepubis is tiny. The femur was considerably shorter than the tibia.

Istiodactylus latidensIstiodactylus latidensBMNH R 3877 (Hooley 1913, Ornithodemus” latidens; Howse, Milner and Martill 2001) ~56 cm skull length, Aptian, Early Cretaceous ~130 mya was an unusual ornithocheirid known from a partial skeleton. Distinct from SMNK PAL 1136, the skull of Istiodactylus was a quarter smaller than SMNK 1136 PAL and similar in size to Coloborhynchus. The long gracile skull was dominated by an antorbital fenestra comprising 63 per cent of its estimated length. The anterior margin of the antorbital fenestra was posterior to all teeth, which fill only the anterior fourth of the jaws. Both narial openings (per side) were dorsal to the teeth. The long quadrates were so inclined that the orbit was positioned even further posteriorly than in PAL 1136. The teeth were lancet-shaped, closely spaced, and interlocked like a bear trap. A central dentary tooth filled the gap left by the medial premaxilla teeth, which were diminutive. The teeth increased in size posterolaterally. Two posterior dentary teeth fit into slots in the premaxilla. The dorsal vertebral transverse processes were nearly vertical. A notarium of six vertebrae was present. Asymmetrical coracoidal articulations on the anterior edge of the deep sternal complex keel continued on the lateral surface. The reconstructed wing/torso ratio was estimated at ~9:1. The deltopectoral crest was warped into a spiral. The ulna had a ridge that supported the radius. The antebrachium was relatively longer than in PAL 1136. What Hooley (1913) identfied as an ischium is identified here as the pubis and ischium.

Figure 3. Click to enlarge. Istiodactylus

Istiodactylus sinensisIstiodactylus sinensisNGMC 99-07-011 (Andres and Ji 2006) Aptian, Early Cretaceous ~125 mya, ~35 cm skull length, appears to be more primitive in that the deltopectoral crest was not so curved and the skull was not as gracile. As in Nurhachius, when the wing was folded the elbow was closest to the middle of m4.2. The three free fingers each had only one phalanx, probably via fusion because there is no dimunition of the finger lengths. The resulting proximal phalanges are all subequal, approaching the configuration inColoborhynchus, which had no phalanx fusion. Only pedal digit I and IV are known and they follow the pattern of larger medial digits seen in sister taxa.

In summary
This clade originated with a big crest on the rostrum tip and a small antorbital fenestra. As taxa evolved the crest slowly disappeared while the antorbital fenestra elongated anteriorly and pushed the orbit higher and smaller posteriorly.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

ReferencesAndres B and Ji Q 2006. A new species of Istiodactylus (Pterosauria, Pterodactyloidea) from the Lower Cretaceous of Liaoning, China. Journal of Vertebrate Paleontology, 26: 70-78.Bowerbank JS 1846. On a new species of pterodactyl found in the Upper Chalk of Kent P. giganteus). Quarterly Journal of the Geological Society 2: 7–9.Bowerbank JS 1851. On the pterodactyles of the Chalk Formation. Proceedings of the Zoological Society, London, pp. 14–20 and Annals of the Magazine of Natural History (2) 10: 372–378.Bowerbank JS 1852. On the pterodactyles of the Chalk Formation. Reports from the British Association for the Advancement of Science (1851): 55.Fastnacht M 2001. First record of Coloborhynchus (Pterosauria) from the Santana Formation (Lower Cretaceous) of the Chapada do Araripe, Brazil. – Palaontologische Zeitschrift 75(1): 23-36.Frey E and Martill DM 1994. A new Pterosaur from the Crato Formation (Lower Cretaceous, Aptian) of Brazil. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 194: 379–412.Hooley RW 1913. On the skeleton of Ornithodesmus latidens. An ornithosaur from the Wealden shales of Atherfield (Isle of Wight)”, Quarterly Journal of the Geological Society, 69: 372-421Howse SCB, Milner AR and Martill DM 2001. Pterosaurs. Pp. 324-335 in: Martill, D. M. and Naish, D., eds. Dinosaurs of the Isle of Wight, The Palaeontological AssociationOwen R 1861. Monograph on the fossil Reptilia of the Cretaceous Formations. Supplement III. Pterosauria (Pterodactylus). The Palaeontographical Society, London. (volume for 1858; pp. 1–19 & pls 1–4)Owen R 1874. A Monograph on the Fossil Reptilia of the Mesozoic Formations. 1. Pterosauria. The Palaeontographical Society, London. pp. 1–14 & pls 1–2.Wang X, Kellner AWA, Zhou Z and Campos DA 2005. Pterosaur diversity and faunal turnover in Cretaceous terrestrial ecosystems in China. Nature 437 (7060): 875–879. doi:10.1038/nature03982. PMID 16208369.